Television system



Oct. 18, 1938. vv. K. zwoRYKlN 2,133,882

TELEVISION SYSTEM Filed Marcnso, 1955 5 sheetssneet 1 @n 4I+ l' Il"r m m -I- E Q s 5. n' 2 D vn N D n: s

@et 1s, 1938. v. K. zwbRYKlN 2,133,882

TELEVISION SYSTEM Filed March 30, 1935 5 Sheets-ShamI 2 POWER Witness: 4

` SUPPLY BY@ 2 Oct. 18, 1938. v. K. zwoRYKlN, 2,133,882

TELEVISION SYSTEM Filed March so, 1935 5 sheets-sheet s 18,1938. v KI ZWQRYK|N 2,133,882

TELEVISION SYSTEM Filed March 50, 1935 5 Sheets-Sheet 4 E E E wr\` A u :j ,E /m 'A /d POWER 104 .D- C. CONTROL 'UPPLY'* AMPLIFIER I I 1% fo Y E I/vvE/v'roR Vl adimz r IlZLz/orylin,A

HT'T'OHNEY" Wi incas:

v. K. zwoRYKlN TELEVISION SYSTEM Filed March so, 1955 5 Sheets-Sheet l 5 POWER SUPPLY Vadim ir KZ www .D.C. C/VTHOL HMPL/F'IER INVEN''OH warylin ATTORNEY Patented 50ct. 18, 1938 TELEVISION SYSTEM Vladimir K. Zworykin,

or to Radio Corporati tion oi Delaware Philadelphia, Pa., assignon of America, a corpora- Application March 30, 1935, Serial No. 13,792

2 Claims.

My invention relates to improvements in television systems and the method of operation thereof.

In developing picture signals for television 5 transmission, a scanning device is exposed to light from the view or object for transmission. One form of scanning device for this purpose comprises a'tube having a mosaic, photosensitive screen upon which an image of the View is projected through a suitable lens system. The tube is provided with means for developing a ray of electrons and directing the same at the screen. The ray is deected simultaneously in different directions to scan the screen, whereby the picture signals are developed for supplyto an amplier and transmitter. In such a system, it has been found that the cathode ray transmitter tube operates most einciently under a given condition of illumination by light from the View for transmission and, for this reason, manual adjustments have been made heretofore for the purpose of maintaining the tube at its most eiiicient point of operation as the light intensity, to which the photosensitive screen is exposed from the view, might vary due to occurring changes at the transmitting station such as a change in light intensity from the view, or a change in the distance between the transmitting tube and the view.

o With the foregoing in mind, it is one of the objects of my invention to provide an improved television transmitting system of the character referred to in which means are provided for automatically controlling the light intensity to :5 which the scanning device is exposed from the View, whereby the device is maintained substantially at its most efficient point of operation.-

Another object of my invention is to provide a system of the type described wherein electrical 0 means are utilized for correlating the sensitivity of the scanning device to the degree of illumination of the object being scanned.

Other objects and advantages will hereinafter appear.

5 In accordance with my invention, the scanning device and the circuits associated therewith are utilized to generate an electrical eii'ect which varies with occurring variations in the light intensity to which the device is exposed from v y the view for transmission. This eiect is, in turn, utilized to control the light intensity to which the scanning device is exposed from the view, in the sense that the light intensity is made to decrease upon an increase in the electrical coni trol effect and to increase upon a decrease in such eiect.

More specically, in accordance with my invention, a cathode ray tube of conventional design is utilized to develop the picture signalsand an adjustable shutter device is interposed between (Cl. P18-7.2)

the photosensitive screen of the tube and the viewor object for transmission to control the iight intensity to which this screen is exposed from the View. An electrical eiiect is developed which varies with occurring variations in the light intensity from the view, and is used to cause openingor closing movement of the shutter device, as might be required, to maintain the value of light intensity on the screen substantially at the correct point for most-'efcient operation of Athe tube.

My invention resides in the improved construction and method of operation of the character hereinafter described andY claimed.

For the purpose of illustrating my invention', several embodiments thereof are shown in the drawings, wherein Figure 1 is a simplified, diagrammatic View of a television transmitting system constructed and operating in accordance with my invention; and

Figs. 2, 3, 4, 5, 6 and 'I are views similar toY Fig. 1, showing different modications.

In Fig. 1, the reference numeral lli designates a scanning device in the form of a cathode ray tube of conventional design, comprising a tube i2 provided with a mosaic photosensitive screen lll and with means in the form of an electron gun i6 for developing a stream or ray /I8 of electrons and directing the ray at the screen. The screen comprises a mica sheet provided on the front face 2l! thereof with a large number of minute, metallic, photosensitive elements, spaced and insulated from each other. The

screen is provided on the back face 22 thereof' with a metallic layer to which a connection 2li is made. In operation, an image of the object or view 26 for transmission is projected by a lens system 28 onto the photosensitive surface 2t of the screen. In this way, individual, electrostatic charges are developed over the surface yof the screen, the value of the charge or charges at any elemental area being proportional to the light intensity on that area at the instant.

-The ray i8 of electrons is deected horizontally at a relatively high rate by coils 3U and is simultaneously deflected vertically at a relatively low rate by coils 32, whereby the ray is caused to` scan the photosensitive surface of the screen Hi. In this way, picture signals are developed and supplied by the connection 2c to an amplier 3d and a transmitter 36.

For the purpose of controlling the value of light intensity to which the screen hi is exposed from the view. a shutter device in the form of anadjustable iris diaphragm 38 of. conventional design vis associated with the lens system 28. The opening in the diaphragm 38 is made larger or smaller upon rotation of a gear 40 which meshes with a pinion 42 ilxed on a shaft 44 driven by aD. C motor 46. The motor 46 is provided with separately excited eld coils 48, as represented in the drawings, and is also provided with a suitable brake 50 which places a relatively light, initial load on the motor.

The amplified picture signals from the amplier 34 are supplied by a connection 52 to the grid of a relatively high impedance electron tube 54 of the type identiiied in the trade as RCA 57". The tube 54 has a self-bias resistor 56 of relatively high resistance. 'Ihis resistor is shunted by a condenser 58 of relatively high capacity. In operation, a D. C. voltage is developed across the resistor 56 which varies substantially in accordance with occurring variations in the average peak A. C. voltage on the grid of the tube 54. This tube and its associated circuits operate at a peak Voltmeter. An electrical effect, accordingly, is developed which varies with occurring variations in the light intensity to which the screen I4 is exposed from the view. This electrical effect is ampliiied by a control amplifier -68 to develop a voltage across a resistor 62 in the output circuit of a tube 64 forming part of the amplifier.

The motor 46 is supplied from the amplifier 68 through connections 66 and 68, a battery 18 being connected as shown in the connection 68.

Iii)

. movement ofthe diaphragm 38.

Adjustments are made initially so that when the Value of light intensity to which the screen I4 is exposed is substantially correct for most ei'c1ent operation of the electron scanning device I0, the potential difference Vm between the potentials Va and Vb is substantially zero, or at least so small as to prevent operation of the motor 46 against the drag orload provided by the brake 50. If illumination of the Ascreen I4 should increase, the potential Va increases correspondingly to give a, Value to the potential Vm to cause rotation of the motor armature in the proper direction to cause closing movement ci' the iris diaphragm 38. 'I'his action continues until sufficient light is cut off from the screen I4 to bring the value of the potential Va back to the point whereat the potential Vm is at least lowenough to permit the brake 50 to stop the motor. If illumination ofy the screen I4 should decrease below the desired value for most emcient operation, the reverse action takes place. 'I'hat is, the potential Va decreases and becomes lessv than the potential Vb, whereby the polarity across the lines 66 and 68 is changed and the po tential Vm becomes at least Suillcient to cause reverse -rotation of the motor to cause opening This action continues until the screen I4 is again exposed to the equired light 'intensity from the object for mostv eiiicient operation, at which time the potential Vm again becomes zero, or at least decreases to a value insufcient to cause rotation of the motor against the braking action of the brake 50.

The brake 50 provides for suillcient time lag to prevent actuation of the diaphragm 38 for every slight-momentary change in illumination of the screen. I4.

From the foregoing it will be seen that variation in the peak picture signals, with occurring Variations in illumination of the screen I4, is utilized to develop an electrical control eect which varies in a similar manner and operates to control adjustment of a shutter device interposed between the scanning device and the view,

whereby the value or degree of illumination of the scanning device is changed accordinglyto bring it back to the point forv most eilicient oper- I ation. Y

In Fig. 2, the operating action is the same as that in Fig. 1 except that the electrical control effect is obtained from the second anode 'I2 of the transmitting tube. The principle involved resides in the fact that the photoelectric current, taken from the anode 12, varies proportionally to occurring variations in the degree of illumination of the screen I4. For the purpose of adjusting the diaphragm 38, a solenoid I4 is utilized instead of the motor in Fig. 1. The solenoid is connected by levers 16 and 18 to the actuating member of the iris diaphragmv 38. A piston 88 is connected as shown to-the solenoid, .and is disposed within a cylinder 82 provided at one end with a vent opening 84. A coil spring 86 is disposed between the piston and the other end of the cylinder. Adjustments are made initially so that the degree of illumination of the screen I4 is correct for most eicient operation, in which case the voltage across the lines 66 and 68 is sufficient to operate the solenoid so that it holds the diaphragm 38 open *at the right point, against the action of the spring 86 which is compressed. If the degree of illumination of the screen I4 drops below the desired point, the potential across the lines 66 and 68 will drop correspondingly to lessen the downward pull of the solenoid 14. The spring `86 is then eiective to cause movement oi. the lever 16 to open the diaphragm 38 until illumination of the screen I4 is again sufiicient to cause the downward pull of the solenoid 14 to balance the upward force due to the spring 86. If the degree of illumina- A tion of the screen increases beyond the point desired, the reverse action takes place. That is, the potential across the lines 66 and 68 increases so that the downward pull of the solenoid 14 is suilicient to further compress the spring 86, whereby the diaphragm 38 is caused to close. 'This action continues, as will be well understood, until the degree of illumination of the screen I4 is again such that the downward pull of the solenoid 14 is balanced by the upward force due to the spring 86.

'I'he piston 80 and cylinder 82 operate as a dash-pot and, with the vent 84 at the proper size, serve the same purpose as the brake 50 in Fig. .1 to provide a time-lag.

In the system shown in Fig. 3, both the control electrical eiects in Figs. 1 and 2 are utilized to control the motor 46 for adjusting the diaphragm 38. 'I'hat is, both the effects of variation of the peak picture signals and the photoelectric current from the second anode 12 are utilized for obtaining the automatic control of light on the screen I4. In this ligure, the various parts and connections corresponding, respectively, to those in Figs. 1 and 2, are designated by the same reference numerals as the latter. In Fig. 3, itis proposed to employ variable ,resistors 88 and 80, connected in the circuit as shown, for the purpose of adjusting the amplitude'of the control amplifier 60. Also, the control signalsl from the anode 12 are ampliiled by an amplier 8| before being supplied to the ampliner 68.

In Fig'. 4, the control electrical effect is obtained by supporting a photoelectric cell 82 adjacent 4the screen I4y so that it is exposed to the light emitted therefrom.- In this way, an electrical control eiect'is developed which increases when the degree of illumination 'of the screen I4 exceeds that required for most efiicient operation, and decreases when the degree o1 illumination of the screen falls below the desired value. The control current from the cell 92 is ampliiied by the control ampliier SB and is eiective to cause operation of the motor i6 in the same manner and for the same purpose as in Fig. l.

The arrangement and operating action of the system shown in Fig. 5 is the same as that in Fig. 2 except that an additional connection 9d is made from the output of the control amplifier 6E to the control grid B of the electron gun. The polarities are such that as conditions change to call for further opening of the diaphragm 38, the blason the grid S5 is decreased to increase the intensity of the scanning ray correspondingly. When conditions change to call for closing of the diaphragm 38, the bias on the grid St is increased correspondingly to decrease the intensity of the scanning ray.

In Fig. 6, the scanning device is represented as being in the form `of a cathode ray tube of conventional design in which the mosaic, photosensitive screen ida is two-sided. That is, the minute, metallic elements,l represented-anse, pass through the supporting mica sheet, and are photosensitive on the side removed from the electron gun. In operation, an image of the view is projected onto the photosensitive surface of the screen ida through a wire meshiD which is maintained at a potential positive with respect to the potential of the screen illu. The principle involved restles in the fact that the sensitivity of the tube varies upon variation in the potential on the anode IBD. The control electrical eiect is obtained, as in Fig. 2, from the second anode 72a, and is supplied to the control amplifier $0. The potential on the anode lilo is dependent upon the voltage across the resistor md in the output circuit of the amplifier Si?.

In operation, adjustment of the potentiometer' IBS is made to bias the anode 109 to the point for most emcient operation. Ii the degree of illumination of the screen Ilia decreases below this point, the voltage across the resistor |04 charges to cause the potential on the screen |00 to become more positive with respect to the potential on the screen ma. In this way, the sensitivity of the tube is increased until the point is reached whereat the tube is again operating most eficiently. If the degree of illumination of the screen 98 increases beyond the desired point, the automatic control action is just the reverse. That is, the potential on the anode |00 becomes less positive with respect to the potential on the screen Ida to decrease the sensitivity of the tube, until conditions are again restored to the point for most eicient operation.

In Fig. '1, the transmitting tub" is shown as being provided with an auxiliary source of electrons, designated generally by the reference numeral I 08, and comprising a iilament l IU, a grid H2, and an anode HB. By this means, electrons in the form of a spray are directed at the screen iE to supply a bias thereon. In operation, as the degree of illumination of the screen M decreases below the point for most eicient operation, the control signals, which in this case are taken from the second anode 12 and supplied to the control ampliner Se, are effective to cause the potential on the anode HB to become less positive, whereby the velocity oi electrons from the source I 88 decreases correspondingly. The screen It then collects more primary electrons 'than it emits secondary electrons, so that the individual, photosensitive elementsv become more negative, and the tube becomes correspondingly more sensitive. A

When the degree of illumination of the screen l# increases beyond the desired pointfthe action is just the reverse. That is, the potential on the anode iid becomes more positive to causea corresponding increase in the velocity of electrons from the source M3. Since the electrons from this source now strike the screen M at a greater velocity, more secondary electrons are emitted therefrom than primary electrons, and the minute, photosensitive elements become less negative. The sensitivity of the tube is thereby decreased until it is again operating at the desired point.

'Ihe values of operating potentials, resistance and capacity may be substantially as designated` in Fig, l. These values, however, are not critical,

and may be varied over a substantial range, as

might be required.

From the foregoing it will be seen that I have provided an improved television transmitting systern and method of operation thereof in which adjustments are automaticalLv made as the degree of illumination of the scanning device might vary due to change in illumination of the object, or change in the distance of the transmitting tube from the object, and that in this way the system is maintained at substantially the point for most emcient operation thereof.

It will be understood that modications, other than those disclosed, are possible without departing from the spirit of my invention or the scope of the claims.

I claim as my invention:

1. In a television system, a cathode ray transmitter tube comprising a screen which is so sensitized that it emits electrons when an image is formed thereon, said tube also comprising an electrode positioned to collectk said electrons and further comprising means for producing a cathode ray, means for scanning said screen by said cathode ray whereby picture signals are developed, a connection including an impedance unit between said collector electrode and said ray producing means, a shutter device for controlling the intensity of said image, and means including a direct current amplier connected between said impedance mit and said shutter for decreasing the intensity of said image in response to an increase in the `voltage drop across said impedance unit.

2. In a television system, a cathode ray transmitter tube comprising a screen which is so sensitized that it emits electrons when an image is formed thereon, said tube also comprising means for producing a cathode ray, means for scanning said screen by said cathode ray whereby picture signals are developed, means for producing an electrical eiect which varies in respense to occurring variations in the intensity of said image, a shutter device for controlling the intensity of said image, means for controlling said shutter device in accordance with said electrical eiect in the sense that the shutter device is caused to close in response to an increase in the intensity of said image, and means for simultaneously increasing the intensity of said cathode ray in response to an increase in the intensity of said image.

VLADEHIR. K. ZWORYKIN. 

